1. Field of the Invention
The present invention relates generally to distraction devices for use in medical procedures. More particularly, the present invention relates to subcutaneously implantable distraction devices.
2. Related Art
The need to apply distraction, or separation, forces is often required in a variety of medical procedures. For example, treatment of conditions such as congenital deformities, limb length inequalities, traumatic bone defects, and mal-alignments of the skeleton often require that bones or bone structure be moved to, and/or held by force in, a particular position for a particular duration of time. Many conventional distraction devices are primarily external devices, that is, much of the structure includes fixators and frames disposed outside of a patient's body. Examples of such external devices include the Ilizarov fixator and the Taylor Spatial Frame.
While such external devices have been used with some degree of success, they have proved problematic in a number of areas. For example, such external devices generally require percutaneous hardware that connects the external components of the devices with the internal components of the patient's skeletal structure. The presence of hardware running through the skin can lead to higher incidents of infection. Also, externally exposed hardware is susceptible to impact during ordinary activity, which can damage the hardware and/or compromise the hardware installation.
In addition to these known external devices, some distraction devices have been developed which incorporate internal fixation hardware. That is, such devices are at least partially implantable beneath a patient's skin. One such example is sold under the mark Titanium Rib® by the Synthes Corporation and was developed by Robert Campbell. This technology is the subject of Canadian Patent No. 2,051,665 and is often used to treat Thoracic Insufficiency Syndrome.
The Campbell device is generally comprised of two overlapping metal slats which attach at opposing ends to two rib elements. To install the device, an incision is made in a patient and the two slats are generally individually attached at opposing ends to two spatially distant rib elements. The ribs are distracted by forcibly extending the two slats to a desired length, at which point the length of the device is fixed by attachment of a complex latch mechanism to each slat. The incision is then generally closed. When it is desired to distract the two ribs to a greater extent, the patient is “opened” again and the latch mechanism is removed from the two slats. The two slats are then again forcibly extended and latched in position.
While such internal devices have proved successful in some applications, they have typically proved problematic in that the devices must be surgically exposed by incising the patient's skin each time an adjustment is made. Once exposed, the devices must be manually adjusted to a desired length. Finally, once the adjustment procedure is complete, the incision must be closed and allowed to heal. Accordingly, the adjustment procedure for such devices has proved overly complicated and prone to the problems inherent in general surgical procedures. In addition, such devices are generally limited in the available range of distraction, as the devices have a maximum extension length, that, once reached, requires that the device be completely removed and replaced with a similar device with a greater extension length.